1. Field of the Invention
The invention relates in general to mining devices and methods and in particular to a new and useful method of and apparatus for producing underground cavities in a driving operation using a shield advance.
2. Description of the Prior Art
To produce underground cavities, for example, in the construction of tunnels, adits, or caverns, the conventional shield tunneling method provides that a shield is mechanically advanced into the ground. In this operation, considerable frictional forces are produced between the shield and the ground which are absorbed, through hydraulic pressure devices, by the following lining. The inner core is then mechanically excavated under the protection of the shield. What is disadvantageous in this method is that the shield advance causes a compression of the surrounding ground in the zone, frequently resulting in a heave of the formation ahead of the work, which becomes manifest during the further advance in a loosening of the rock structure, and this may lead to damaging subsidences. Also, the surrounding formation is thereby considerably disturbed. Another disadvantage is that the lining, mostly tubbings, must withstand the high pressures occurring during the intermediate stage of construction, so that usually it is to be oversized with respect to its final function. In consequence, notwithstanding its advantages in driving operations with mechanical excavation and lining, the conventional shield tunneling method cannot meet the requirements of the New Austrian Tunneling Method, in which the natural supporting strength of the formation is to be maintained to a large extent by preserving the grown structure of the rock, and the cavity is secured by a thin-walled lining. Moreover, the application of the conventional shield tunneling method is limited to loose rock formations.